In the article "Phase-locked loop design fundamentals" with the Application Note AN-535 issued by Motorola Semiconductor Product Inc, voltage controlled VCXO crystal oscillators included in phase changing arrangements are described. These generate an output signal for synchronising different digital units. The known calculating unit includes an analog regulating filter and a charge pump controlled by a phase detector, and has its control signal output connected to the regulating voltage input on the oscillator. An analog controlled VCXO oscillator is about five times more expensive than an XO standard oscillator, which generates a signal of fixed frequency without any regulating capacity. The use of commercially available VCXO oscillators also brings with it as technical disadvantages that the generation of the analog regulating voltage obstructs digitalisation of the phase changing arrangement, and that the frequency adjustment range is limited.